The increasing awareness for the reduction of environmental damage caused by synthetic polymers is contributing to the growth of sustainable biopolymer sectors. In the last decade, numerous research resources have been devoted to replace the fossil-based polymers available in the commercial markets. Biobased polymers are positioned as one of the most promising solutions to reach sustainable development due to their reduced environmental impact. Nevertheless, the constant usage of polymers in building structures, the automotive industry, and many other industrial/commercial applications, has increased the fire hazards of everyday life. Therefore, flame retardant biopolymers have attracted much interest in the last few years.
The typical fire retardants (FR) used in polymers reduce the burning rates by interrupting the fire cycle in any of the heating, pyrolysis, ignition or combustion stages. Recently there have been many concerns about toxicity, environmental and recycling issues as a result of the FR decomposing into more toxic substances. After the banning of many toxic materials, Biobased FR have emerged as materials with unique potential. In the last years, nano-clays have attracted much attention in the flame retardant field. Amongst them, halloysite nanotubes (HNTs), a typical kind of nano-clay, with a high aspect radio that allows them for easy hybridization with fire retardant elements such as nitrogen and phosphorus. In addition, HNTs may also provide multifunctional properties to polymers due to their potential in other fields and as reinforcement materials.
In this dissertation, a Biobased polyamide (PA-56) was selected as the polymer matrix and the halloysite nanotubes (HNTs) were chosen as the reinforcement material. By adding phytic acid or chitosan, it was possible to enhance the charring capacity of the composites, the combustion properties achieved an important reduction of the peak heat release of 47% and a delay of 100s in the combustion times. The significant increase of fire retardancy was attributed to the barrier effect of halloysite nanotubes, and the catalytic carbonization process of phytic acid during the formation of the char layer. SEM evaluation confirmed that a compact structure char layer was formed. Also, the thermal stability was tested by TGA, after the addition of the pure and modified HNTs the degradation temperatures (T-5wt.%, T-max) and char residue at 700 °C were notably increased. The findings of this study suggest that it is possible to decrease the FR loading, enhance the fire retardant and mechanical properties of polymer composites without compromising their toxicity and biodegradability.